Conventionally, fluorocarbon (called “FC” below) has been mainly used as a refrigerant in refrigeration systems, and in recent years, the development of technology using carbon dioxide has progressed. In the field of in-vehicle air conditioners, air conditioners that use carbon dioxide as a refrigerant such as described in Japanese Patent Publication No. 2001-74342 have become publicly known, and in the field of hot water supplying devices, products that use carbon dioxide as a refrigerant are commercially available.
On the other hand, in the field of air conditioners for homes and air conditioners for commercial use, currently development is at the stage where it is progressing and has not reached the stage of commercialization.